Add flow visualization for tool builder

Implements node-based flow visualization using NodeGraphQt-QuiltiX-fork:

New files:
- src/cmdforge/gui/widgets/flow_graph.py: FlowGraphWidget with custom node types
  - InputNode: Shows tool inputs ($input + argument variables)
  - PromptNode: AI prompt steps with provider display
  - CodeNode: Python code steps
  - OutputNode: Final output
- scripts/test_nodegraph.py: Standalone prototype for testing

Modified files:
- tool_builder_page.py: Added List/Flow view toggle with QStackedWidget
  - Lazy-loads flow widget on first use
  - Syncs between list and flow views
  - Double-click nodes to edit steps
- styles.py: Added viewToggle button styling
- widgets/__init__.py: Export FlowGraphWidget
- pyproject.toml: Added 'flow' optional dependency group

Features:
- Toggle between List and Flow views in Steps panel
- Nodes auto-connected based on step order
- Auto-layout and fit-to-view on load
- Double-click nodes opens step edit dialog
- Graceful fallback if NodeGraphQt not installed

Co-Authored-By: Claude Opus 4.5 <[email protected]>

pyproject.toml

@@ -46,11 +46,17 @@ registry = [
     "sentry-sdk[flask]>=1.0",
     "gunicorn>=21.0",
 ]
+flow = [
+    "NodeGraphQt-QuiltiX-fork[pyside6]>=0.7.0",
+    "setuptools",  # Required for distutils compatibility
+]
 all = [
     "Flask>=2.3",
     "argon2-cffi>=21.0",
     "sentry-sdk[flask]>=1.0",
     "gunicorn>=21.0",
+    "NodeGraphQt-QuiltiX-fork[pyside6]>=0.7.0",
+    "setuptools",
 ]
 
 [project.scripts]